Pulse transmission system



1945- c. w. HANSELL 2,381,445

PULSE TRANSMISSION SYSTEM Opiginal Filed Dec; 2 7, 1940 2 Sheets-Sheet l TRANSMITTER INCLUDING S/GNAL MODULATOR INVENTOR CMREVC'F W AMA/$621 ATTO R N EY 1945' c. w. HANSELL PULSE TRANSMISSION SYSTEM Original Filed Dec. 2 Sheets-Sheet 2 INVENTOR CZAREA/CE M. INA/SELL BY 6 MUM ATTORNEY tion of slowjsp'eed facsimile signals.

-.,in. from 'thetransmitter.

"iii-12,3 1,445 PULSE TRANSMISSIbN srsr z Clarence Hansell', Port Jefferson, N.;Y.,'assignor to Radio Corporation .of ration of Delaware America, a, 0011901 I Original application December 27', 1940, SerialNo.

371,865. Divided and this'applicationdune 30, 1942,Seria1 No; 449,064

; 17 Claims. (o1. 350 17) This invention is a division of, my copending application Serial No. 371,865,: filed December 27,

he present invention relates to improvements i n' -r'adio communication, and has'f or its primary f Jobject to improve the signal-to-noiseratio of radio systems. A further object is'to obtain the aforesaid improved signal-to-n'oise ratio Without increasing the -size of the vacuum tube equipment furnishing the power to th'e radio transmitter. I The invention isprimarilygapplicable to radio systems for the transmission and reception of I "telegraph signals, including "printer signals, and

may also be used for the transmission and recep- The objects of the present invention are achieved, in brief, by radiating from the trans- 'fmitter short pulses of increased power (i. e.', in-

" creasedrelative to the permissible steady state value) and conditioning'the receiver to be jresponi've substantially only during th'e intervals when energy is coming in from the transmitter.

;to produce pulses or bursts of power. By maieating all the stored output power in relatively short periods oftime compared to the intervals between radiation periods, there is obtained an:

' increased. power output compared to a normal steady state value of 'power output. The normal ofth e inventiondepend'-upon its accuracy or otherwise;

can consider the signal-to-no-ise power ratio'in radio circuits as ratios of energy flow per V unit of time. general, the total noise energy in the output of a receiver is proportional to 'noise power multiplied by time. If the time during which a receiver is operative is reduced to --10%', the total noise energy and average power in 10' the output of the receiver will'also be reduced to 10%. "Thatis, a receive which is controlled in such a'wlayas to be responsive during intervals of 5 0 :of a'second repeated at a rate of 500 cycles, will have a'noise in its output reduced by about ten toone in power. If the repetition rate M is reduced to 50, still maintaining /5000 second as the responsive period of the receiver, the noise power,*or energyrate, in the output of the renoise ratio when used on an ordinary signal besteady state'valueis the' power output which'rthe transmitter can deliver continuously. At the receiver, the frespo 'n se period is, timed synchrol nously with the transmitter so that the receiver. givesan output which'is caused only by the enany noise which existsbetWeenperiods-of signal input to the receiver is prevented from contributing to noiseoutput from the receiver. Inthis way, no noise is permitted to build up energyin the selective circuits Of'the receiver except that 'Which' exists'whilethe receiver circuits are recep- :tive or ,;open. During these open periods of I the receiver, the signal, with its increased power,

makesits greatest impression; 1

f;, ;In order that the-present invention maybe better. understoodfan explanation of r the theory underlying the-invention will now begiven. "While this. xplanation. is believed to be. correct; it is not of, necessity complete, nor does th'e operation same ratio as the noise.

steady state value of an ordinary signal.

cause the useful signal will be reduced in the However, by storing up the output power from the transmitter and then radiating it all in second bursts at times synchronous with the receiver responsive period and with correct timing between transmitter and receiver so that" the signals arrive at the receiver when it is responsive, then there' can be obtained an improvement in signal-to-noise ratio. This 'isgenerally what is done in the present invention.

. If, for example, we have a transmitter which hasan available output of about 200 kilowatts, and the transmitter power output were stored up and then used during -of a second intervals,

repeated at a 500cyclerate, then the signal-tonoise ratio would be improved as thoughthe transmitter powerhad been increased from 200 kilowatts-to 2000 kilowatts.v By storingup the transmitterpower output, we are, in effect, enabledto release at the pulse period a power output which in-fact greatly exceeds the normal If'the pulse period is T 6 of the total time used for transmission, then theoretically it is possible to send outduring pulse periods I I ten times the power output of the steady state signal. This is because the'rate of change of stored energywhen being {transmitted during pulse periods is'very' much greater thanthe rate of} change. of stored energy during, off periods earns when the transmitter is delivering power to the storing oscillatory circuit. If, in the immediately foregoing example, the repetition rate were reduced to 50 cycles, then the power output during the active periods would be equivalent to 20,000 kilowatts. By employing circuits having suitable antenna power gains due to the use of a directive antenna, it is possible to still further increase the signal-to-noise ratio. Anantenna power gain of 100 to 1, for example, would increase the effective power to 2,000,000 kilowatts.

Although at first blush it might be thought -mitter, lose efficiency at very high frequencies due to time lags in breakdown of theair in the spark gaps. Under some circumstances, however, it might be possible to use a timed spark type transmitter, although such an arrangement is not preferred to carry out the purposes of the invention. According to the present invention, it is proposed to employ low power factor oscillating circuits for storing energy in the trans nutter. Such circuits may be of, the concentric resonant line type now well known in the art. They may also :be resonant metal enclosed cavities, known as cavity resonators. These'low power factor circuits may be fed with energy continuously from a continuous wave transmitter during periods when transmission is desired, and energy for the antenna may be drawn from these low power factor circuits during short time intervals at a rate considerably higher than the transmitter could deliver directly. As an illustration, it is practical to obtain resonant line low power factor circuits with the power factor due to losses in the line itself of about one part in 20,000 (Q=20,000)-. Of course, different and higher values of Q are attainable with special design of the circuit elements.

The following is a detailed description of the invention accompanied by drawings, wherein:

Fig. 1 illustrates, in abbreviated form, the essential circuit elements of a transmitter for transmitting short pulses of energy in accordance with the principles of the-invention;

Figs. 2 and 2a are details showing two different forms of the toothed disc wheel which can be employed in the transmitter of Fig. i; and

Fig. 3 illustrates the principles of the invention applied to a complete radio communication system having a transmitter and a receiver.

Referring to Fig. 1, there is shown a high frequency radio telegraph transmitter I whose out-- put is fed to the transmitter output coil I"! from which energy is passed through half wavelength (M2) line sections3, 3 to a half wavelength (M2) resonant line 4. Output from the half wavelength resonant line '4 is supplied to the antenna 1 through variable coupling condensers. provided by plates 5, 5 in cooperation with a toothed wheel or disc 6 and also through coils II and transmission line l2. Transmitter I and its out-- put coil H are surrounded by a grounded metallic shield l5, while the half wavelength line sections 3, 3 and the half wavelength resonant line 4 are respectively shieldedby means of surrounding shields I6 and I3. The line sections 3, 3 are each one-half wavelength long a measured from the points of connection on the output coil I! to the points of connection on the half wavelength resonant line 4. Obviously, the electrical length of the line has been referred to, since the physical lengthmay be something more or less than this, due to end effects and so forth. The connections of the line section 3, 3 to the coil I! and to the resonant line 4, are, it should be noted, symmetrically arranged with respect to the center or nodal points on these elements. Similarly, the connections from the resonant line 4 to the condensers constituted by the plates 5, 5 are also symmetrically arranged and on opposite sides of the mid point or nodal-point on the resonant line.

The toothed disc 6 is driven by means of a hub l0 and a shaft 9 connected to a motor (not shown), at an exact speed, which ma be done by controlling a synchronized driving motor, to which the shaft 9 is linked, from an extremely accurate frequency standard. This is described in more detail in connection with! Fig. 3. This toothed disc is made primarily of insulation and has metal teeth symmetrically arranged on opposite, sides of the shaft and may take any one of the forms indicated in Figs. 2 and 2a. Each tooth'in the disc 5 is a desired percentage, let us say somewhat less than 10%, of the total distance around the periphery. When one metal tooth is loetweenthe plates 5, 5 of one condenser, the other metal tooth will be between the plates 5, 5 of the other condenser on the opposite side of the wheel E. Thus, these condensers 5, 5 have maximum capacity when a metal tooth happens to be positioned between the plates, and at this time will permit the delivery of near maximum output from the half wave resonant line 4 to the antenna I. For low values of capacity of the condensers 5, 5, the output is made very low.

It will thus be noted that the capacity of these condensers is varied by means of the toothed wheel 6 which is so designed and operated that power is fed to the antenna for short periods, let us say, of 5000 second repeated at intervals of /500 of a second. Both condensers will have maximum capacity simultaneously, and also minimum capacity simultaneously.

The variable inductors 8, in parallel to the condensers, serve to neutralize the residual capacity of the condensers when no signal or radiation is desired; which will occur between pulses or during idle periods corresponding to the time when spaces between the metal teeth on the wheel or disc 6 are present between the condenser plates. The coils 8, 8 are'adjusted to give the minimum current in the antenna during these no signal or off periods. I

Coils I I, I I are provided in series with the conductors of the feed line I2 inorder to tune out the reactance of the condenser and coil system, 5, 8 when the condensers have a maximum capacity. That is, the coils II, II provide a series short circuit, in the transmission line leads (1. e., minimum impedance therein to energy of the operating frequency) to'enable maximum current to go to the antenna from the half wave resonant line 4.

If the transmitter I were capable of delivering 200 kilowatts, given by way of example only, then the antenna load, when it is effective, should be ableto take up to 2000 kilowatts. The three half wave'line sections 3, 3 and 4 serve as a fly wheel, so to speak, or tank .circuit'to smooth out the by'a crystal; oscillator. 22

dy-ne. detector of apparatus: 2.1;

.cillator: 22 andr frequency divider" 2i. taloscillators andsfrequency dividers atb'oth'the load. fluctuations and therefore hold substantially constant load on the transmitter I...

. vfIZhetoothed wheel condenser arrangement, in order td handle the large amount of power required,,-should preferably be operated in compressed airor in acompressed gas,.such-'as hydrogen, helium, nitrogen, carbon dioxide, etc.,.which should prevent oxidation in-caseof arcing-between condenser plates.- I-f the pressure of the .compressed; gas-be .macle; to be 1500 pounds or about 10.0 atmospheres. the spacing. between the elements in the condenser might be reduced to something like-1% or. lessof that permissible in open airt;before there occurs the; danger or arcing. Consequently, for a given capacity,. the area of I the condenser. plates can be reduced to 11% of thatrequi'red inopen: air. Thus, at. 100 atmos- ,pheres the; total volume required for. the working part of 'the.:condenser wouldbe only /1o,00o of that which would be. requirediin. open air. F130;. reduce radiation. due to residual. or mini- ..mum capacity in. the variable condenser, there may be; used, if desired, capacity balancing or neutralization condensers (cries-cross. arrangement). between-the con'denserrplates; aSIlS: com- -monl used inapush pull1 amplifier circuits fora similar purpose, insteadof tuning out the residuaLcapacity by meansiof-the. coils- 8, 8, to form withiit.an-anti-resonant circuit as shown in-Fig. 1.

Fig. shows, in conventionalboxform, 3.100111- plete' radio system of. transmitter and receiver embodying. the principles -.of. the present invention.

Thetransmitter. is designed in ,a manner. shown in Fig. 1 to radiate short pulses or bursts: of signal power from antenna 1.

The; toothed: wheel or, disc li-inv the transmitter is linked by means of its shaft 9-,. and a. speed changing gear if .necessary;-toa synchronized driving. motor 20,

, The receiver includes a suitable: antenna 2b whichfeeds the collected signalenergy. to a suit- Inthis way themotor 21b is. driven contribute tothe receiver selectivity, in which case it will be seen that signal and noise energy delivered to. the selective circuits will be only that-which.- exists during, the short time periods when. the. receiver is not blocked and these. periods are made synchronous with reception of transmittedv pulses. With such a condition; the signal. and noise both have an equal chance at building up energy in the circuits ofthe receiver untilxnear the end of the transmitter on period, at which. timethe blocking at the receiver cuts off, the noiser'while-no signal energy is being received. Under these circumstances, the mean signal-to-noise ratio is 1 directly proportional to the instantaneous transmitter power. No noise is permitted. to build-up energy in the selective circuitsof. the receiver exceptthatwhich exists while-the receiver circuitis-openf which is the period during. which the signal makes its greatest circuits donot follow the pulses in amplitude but instead/maintain a more or less constant energy level, corresponding to the average power of pulse and space. periods. The. selective circuitslsmooth: out on suppress the. pulses but are so designed as to responcl'zto; modulation frequencies-.-lower than the pulse-frequency. The transmitter power mayi thenbeamplitude, phase or frequency modulated. or keyed by. useful: signals,

andthese signals will be reproducedin the receiver output,v with improved .signal-to-noise ratio if. the final receiver detector is. suitably chosen.

, In those. cases where the. instantaneous transmitter powerlies above thenoise' power, at the receiver, the improvement in-signal to noise ratio ableradio frequency amplifier stage and: then to a- ,heterody-ne-- and detector stage 21:. from which intermediate frequency energy is applied ,to az keyed". amplifier stage t8". Oscillator. 3|? is a r heterodyneoscillator fen use with& the: hetero- T-he output of the keyed; amplifier is fed. to a highly selective amplifier system ZQYbefOre'bein'g passed onz to. a final. detector and subsequently to the audio am- .plifier; stages-=31!) (shown conventionally inv box form). lit-order. to :quench; or block." the receiver,

there iszprovicledv a* motor 'Z'OIsimiIa-r to: the motor shown at the transmitterrand whichis drivenin exact. 'synchronism. with 17118511101301. at thetransmitter over alsimilar arrangement of crystal os- Tlie: crystransmitter and receiver are designed to have the samecon'stantsl The motor 20 servesw'toperiodically quench orabloclr the receiver in keyed tive: amplifier. circuit. In the: arrangements just described; the receiver blockingr or quenching is ,done:. a-head; of.those: circuits: which effectively may be. obtained. with a simpler arrangement at the receiver' than that shown in Fig. 3'." The keyed amplifiermay be replaced by. an amplifier so designed. and adjusted, as to provide for a thresholdefiect- That is, the amplifier may provide outputonly when-it is supplied with an in-- putgreater than. some fiXedvalue, which may be the. noise level, but less than the signal level. By. this. means allnoise present between signal pulsestends-to be suppressed.

Although existing frequency standards are so goodthatzsynchronism between transmitter pulses and: receiver quenching may be maintained for long. periods,.I-. contemplate providing manual or automatic timing correction at the receiver in ways. already well known in facsimile and televisioncommu-nication systems.

' *Itis to be understood that the invention is not limitedto'theprecise circuit arrangements illustrated and described; since various modifications may? be'imade without departing from the spirit and scope thereof. As an example; at the transinitter in; orderto relieve the instantaneous load .half wavelength (shown; in Fig. 1).

om the transmitter during on-ofi telegraph keying; at: therbeginning of each. dot and dash, the

line: sections between'the transmitter l and-the half wave resonant line-4 may be made'one-quar stantial maximum of capacity.

over cables, by supersonic mechanical waves, etc.

What is claimed is: I 1. The method of operating a radio transmitter system which includes continuously storing radio frequency energy at said radio transmitter and radiating the stored energy from said transmitter without change in frequency for short time periods compared to the intervals between radiating periods, thereby increasing the maximum 'power output of the transmitter during radiation above the input power.

-2. In combination, a high frequency transmitter, a tank circuit coupled to the output of said transmitter, an antenna, a two-conductor feeder coupling said antenna to said tank circuit, a condenser located between each conductor of said feeder and said tank, and means for periodically increasing the capacity of said condensers simultaneously to substantial maximum and then decreasing the capacity of said condensers simultaneously to substantial minimum, whereby pulses or bursts of power are transmitted to said antenna from said tank when said condensers have a sub- 3. Apparatus in accordance with claim 2, characterized in this that said means for varying the capacity of saidcondensers includes a rotating disc wheel having a pair of metal teeth located on Opposite sides of the center of the disc, said teeth being arranged to pass between spaced plates of said condensers as said disc rotates.

4. In combination, a frequency transmitter, a tank circuit coupled to the output of said transmitter, an antenna, a two-conductor feeder coupling said antenna to said tank circuit, a condenser located between each conductor of said feeder and said tank, and means including a rotating disc wheel for periodically increasing the capacity of said condensers simultaneously to substantial maximum and then decreasing the capacity of said condensers simultaneously to substantial minimum, said wheel having a pair of metal teeth located on opposite sides of the center of the disc, said teeth being arranged to pass between spaced plates of said condensers as said disc rotates, whereby pulses or bursts of power are transmitted to said antenna from said tank when said condensers have a substantial maximum of capacity, and means for neutralizing the'residual capacity of said condensers during the time said condensers are at substantial minimum capacity.

5. Apparatus in accordance with claim 4, including a coil in each side of said two-conductor feeder for tuning out the reactance of said condensers when said condensers have a substantial maximum value of capacity.

6. In combination, a high frequency telegraph transmitter, an output coil for said transmitter, a half wavelength low loss resonant line tank, low loss connections from said tank to said output coil,

. a pair of connections from said resonant line tank mal asthe energy is built up in the one-half waveto a feeder extending to a load, a condenser comprising a pair of spaced plates serially arranged in each of said last connections, a rotatable insulation wheel having two metal teeth therein positioned so that said teeth'pass between the plates of both of said condensers at the same time as said wheel rotates, and means for driving said wheel at an extremely accurate speed, whereby the'relative capacities of said condensers are always substantially the same and change simultaneously in value to the same extent with rotation of said wheel.

7. In combination, a' high frequency telegraph transmitter, an output coil for said transmitter, a half wavelength low loss resonant line tank, low loss connections from said tank to said output coil, separate metallic shields surrounding said resonant line tank and said low loss connections, a pair of connections from said resonant line tank to a feeder extending to a load, a condenser comprising a pair of spaced plates serially arranged in each of said last connections, a rotatable insulation wheel having two metal teeth therein positioned so that said teeth pass between the plates of both of saidc'ondensers at the same time as said wheel rotates, and means for driving said wheel at an extremely accurate speed whereby the relative capacities of said condensers are always substantially the same and change simultaneously in value to the same extent with rotation of said wheel, and means for neutralizing the residual capacity of said condensers when both condensers have substantially minimum capacity.

8. A transmitter including a power storing circuit composed of a tank circuit, means for feeding alternating current power into said tank circuit at a-unifolrm rate,'and means for abstracting power intermittently from said tank circuit without change of frequency and at a power rate lizing the stored energy without change of frequency for very shorttime periods compared to the time intervals between them.

11. In a transmitter, an energy storage circuit, means for storing high frequency current energy in said storing circuit, and means for periodically utilizing the stored energy without change of frequency for very short time periods compared to the time intervals between them.

12. Ina transmitter, means for continuously storing energy in the form of high frequency oscillations in a resonant tank circuit, means for utilizing the stored energy without change of frequency comprising a radiating structure, and means for periodically coupling said tank circuit to said radiating structure for very short time periods compared to the'time intervals between them.

13. In a transmitter, an energy storage circuit, means for supplying alternating current energy to said storage circuit, means forutilizing the energy in said storage circuit without change in frequency comprising an antenna, an impedance network coupled between said energy storage circuit and said antenna, and means for periodically varying the impedance ,of said network between a maximum and a minimum, whereby alternating current energy of the same frequency as the supplied energy is transferred from said storage circuit to said antenna in pulses.

14. A transmitter in accordance with claim 13,

including signal modulating means for modulating the alternating current energy supplied to said storage circuit. I

15. In a transmitter, an energy storage circuit, means for supplying radio frequency'energy, to said storage circuit, means iorutilizing the en- 1 orgy in said storage circuit without change in frequency comprising an antenna, an impedance network coupled between said energy storage circuit and said antenna, and-means for periodically varying the impedance of said network between a maximum and a minimum, whereby alternating current energy of the same frequencyasthe supplied energy is transferred from said storage jcircuit to'said antenna in pulses.

. 16. The method of improving the signal to noise ratio in a signaling system which comprises generating a' carrier wave at the transmitter, modulating a characteristic of'said carrier wave in accordance with modulation potentials, interrupting :the resultant modulated wave to produce equal length pulses of short duration compared to the time interval between pulses, and increas-'- lating agcharacteristic of said carrier wave in accordance with modulation potentials, interrupting the resultant modulated wave to produce equal length pulses of short duration compared to the time interval between pulses, in-, creasing the peak power of vsaid pulses by an amount which is limited only by the ratio of the time interval between pulses'to the time duration of the pulses, and transmitting the pulses'of increased power. I v I CLARENCE W. HANSELL. 

